STC32 Wind Chaser Development Board—UAC Audio Sound Card—USB Sound Card Expansion Module

I. Introduction
This project originated from the STC forum: https://www.stcaimcu.com/forum.php?mod=viewthread&tid=5382&extra=page%3D1. It is
a test hardware developed by STC engineers based on the firmware of the STC32F series sound cards.
The STC32F series supports I2S, naturally leading to applications in the audio field.
It is compatible with the "Wind Chaser" development board based on the STC32F12K54 and can be used directly after installation.
 
II. Applicable Headphones
Since the microphone function is not used, the microphone pin of the headphone jack has been shorted to GND in this project, which can be widely used for the following types of 3.5mm headphones:
(1) 4-segment headphones: Chinese National Standard OMTP (National Standard) wiring sequence
(2) 4-segment headphones: International Standard CTIA (American Standard) wiring sequence
(3) 3-segment headphones: Ordinary stereo
 
Additional knowledge, which is not used in this project for the time being:
Determining the wiring sequence of 4-segment mobile phone headphones:
(1) Determining by color:
The insulator of the OMTP (National Standard) plug is black;
The insulator of the CTIA (American Standard) plug is white;
(2) Determining by impedance
The impedance of the left and right channels to GND is low, ranging from tens to hundreds of ohms; The impedance of the microphone to GND is high, ranging from several thousand ohms; Therefore, it can be determined by measuring the DC impedance with a multimeter.
Taking the AM115 mobile phone headphones I have as an example, the actual measured impedance of the left and right channels to GND is 32Ω, and the actual measured impedance of the microphone to GND is about 2.1kΩ.
 
III. Soldering Recommendations:
The main issue is that the pins of the CS4344 are too dense, making manual soldering difficult. Other components are not difficult.
It is recommended to prioritize soldering the CS4344 before soldering other components.
For manual soldering, if you are like me and can't manage it, I suggest trying the following ultimate tricks:
(1) Soldering iron + desoldering wick + flux + board cleaner: First, solder the CS4344 to the PCB, build up solder on the pins, apply flux, solder the iron at 350℃, use desoldering wick to absorb excess solder, and finally clean with board cleaner;
(2) Soldering iron + heating plate + flux + board cleaner: Solder the PCB pads at 320℃, apply flux, place the CS4344 on it, use the heating plate to melt the solder, and finally clean with board cleaner. Do not over-solder the pads, as this can easily lead to solder bridging.
It is recommended to use a multimeter in continuity mode to check all adjacent pins of the CS4344 to eliminate solder bridging.
Among them, the power supply pins pin9 and pin8 are adjacent. The red probe of the multimeter should be placed on pin9 to avoid the risk of damaging the chip. I soldered one badly, which may be due to this reason; it may also be because I repeatedly heated the desoldering wire to remove the solder, and the high temperature caused the damage.
 
IV. Firmware
The aforementioned STC forum open source STC-USB sound card source code, 2023/12/8 Latest version: (1): 48K/16Bit/Dual Channel I2S Example (2): 48K/16Bit/Dual Channel I2S-DMA Example
Recommended DMA version has been uploaded to the attachment of this project; after testing, it can be used on both computer and mobile phone USB.
Firmware download development board: In addition to using the existing CH340 serial port download tool, the STC32 series has added direct USB download, which only requires a USB TYPE C cable, and does not even require additional driver installation, which is extremely convenient and fast.
How to download firmware using a USB Type-C cable:
 
V. Audio Quality:
Both the DAC chip and the amplifier chip affect sound quality. I think it's okay, and considering the price, it's a great deal.
I'm more concerned about background noise, which is most affected by PCB layout. I can tweak it a bit, but not much, and fortunately, it's almost inaudible in actual testing.
 
VI. Other:
Since there's no potentiometer, the volume is controlled solely by the computer/phone. In my tests, even at 10% computer volume, it was quite loud. Extra caution is needed. I recommend connecting the USB cable, adjusting the volume, plugging in the headphones, and then putting them on; otherwise, a sudden vibration can really hurt your ears.
 
VII. Photos